In an airbag system, there is typically a gas source and an inflatable restraint device, which is commonly known in the safety industry as an airbag. In the event of a vehicle crash, the gas source is actuated whereby gas is rapidly channeled into a folded airbag. The inflated airbag provides an energy-absorbing cushion that affords protection to a vehicle occupant during a crash. The airbag serves to minimize occupant injury by absorbing the kinetic energy of the vehicle occupant in a controlled fashion to minimize the deceleration forces experienced by the vehicle occupant. The lower the deceleration forces experienced on the vehicle occupant's chest or head, the lower the likelihood of injury.
In order for the airbag to function properly, the airbag needs to be fully deployed before the vehicle occupant interacts with the airbag. The vehicle occupant begins interacting with the airbag less than 100 milliseconds after the crash occurred, and thus the inflator must provide inflation gas in an extremely rapid manner to fully inflate the airbag before the vehicle occupant contacts thereof. The rapidly inflating airbag may induce injury on the vehicle occupant if the vehicle occupant is interfacing with the deploying airbag. The rapidly inflating airbag has an inflation force associated thereto, which may be applied to the vehicle occupant if the airbag is not fully deployed before the vehicle occupant interacts with the airbag. Vehicle occupants such as children or small adults may be positioned too close to an airbag module, whereby they may interact with a deploying airbag. Furthermore, an out-of-position adult such as an adult leaning forward before a crash occurs may also interact with a deploying airbag.
A dual stage or multiple stage inflator has been proposed to combat the problem of the rapidly inflating airbag potentially injuring a child, small adult, or out-of-position adult. The dual stage inflator has the flexibility of providing a constant gas flow rate into the airbag similar to the single stage inflator, but the dual stage inflator may also provide varying gas flow rates. A dual stage inflator may have pyrotechnic material, stored gas, or some combination thereof. The pyrotechnic dual stage inflator has two ignition systems and two gas generants, whereby a first ignition system is utilized to ignite only the first gas generant and the second ignition system is utilized to ignite only the second gas generant. The dual stage inflator provides a constant gas flow rate by igniting both the first and second gas generants at the same time. Since the dual stage inflator has two ignition systems, the gas generants may be ignited at different times, which varies the gas flow rate. The second gas generant may optionally be ignited while the first gas generant is burning, and the second gas generant may also be ignited after the first gas generant is no longer generating any inflation gas. The dual stage inflator will completely inflate an airbag like the single stage inflator, but has the advantage of having the ability to have a low onset inflation rate. The low onset inflation rate is beneficial in circumstances where a child or small adult will interact with an airbag while the airbag is being deployed. In these circumstances, the likelihood of the inflating airbag injuring the occupant is reduced because the inflation rate is lowered. Preferably, after the occupant interacts with the inflating airbag, the second gas generant is ignited to fill the remainder of the airbag.
Due to the flexibility of the dual stage inflator to tailor the gas output based upon the size and position of the vehicle occupant, there is a need to design cheaper and simpler dual stage inflators.